1. Field of the Invention
This invention relates to an electrophotographic photosensitive member making use of an organic material. More particularly, this invention relates to an electrophotographic photosensitive member having a photosensitive layer containing a novel polysilane compound capable of imparting an improved electrophotographic performance. The present invention also relates to a process cartridge, and an electrophotographic apparatus, having such an electrophotographic photosensitive member.
2. Related Background Art
Various organic photoconductive polymers including polyvinyl carbazole have been proposed as organic photoconductive materials used in electrophotographic photosensitive members. These polymers are superior to inorganic photoconductive materials in view of film-forming properties, light-weight properties and so forth. Nevertheless, they have not yet attained satisfactory film-forming properties, and are inferior to inorganic photoconductive materials in view of sensitivity, running performance, and stability to environmental changes. As organic photoconductive materials for electrophotographic photosensitive members, hydrazone compounds, triarylpyrazoline compounds and 9-styrylanthracene compounds are proposed as disclosed in U.S. Pat. No. 4,150,987, U.S. Pat. No. 3,837,851, and Japanese Patent Applications Laid-Open No. 51-94828 and No. 51-94829, respectively, which compounds have a low molecular weight. By the use of binders suitably selected, these low-molecular weight organic photoconductive materials have somewhat overcome the disadvantages in film-forming properties which come into question in the field of organic photoconductive polymers, but are not satisfactory in view of sensitivity. In recent years, in order to improve sensitivity to incident light, charge retentivity and surface strength, electrophotographic photosensitive members having a structure wherein the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer are proposed as disclosed in, e.g., U.S. Pat. Nos. 3,837,851 and 3,871,882.
However, as long as the charge transport layer is formed using a conventional low-molecular weight organic photoconductive material, the organic photoconductive material is typically mixed with a certain binder resin when used. Hence, because of the binder resin, the resulting electrophotographic photosensitive member has a low charge mobility, resulting in not always satisfactory sensitivity and performance.
Under such circumstances, polysilane attracts attention as a photoconductive material having a possibility of bringing about the desired electrophotographic photosensitive member.
Examples in which a polysilane is used as a photoconductive material are disclosed in U.S. Pat. Nos. 4,618,551 and 4,772,525 and Japanese Patent Applications Laid-Open No. 62-269964 and No. 3-198061.
According to the disclosure in U.S. Pat. No. 4,618,551, a polysilane compound is applied in an electrophotographic photosensitive member, which is used at a potential as high as 1,000 V, while the surface potential used in usual copying machines is 400 to 800 V by absolute value. This is considered to aim at elimination of spot-like faulty images caused by a structural defect of polysilane. Japanese Patent Application Laid-Open No. 62-269964 also discloses the production of an electrophotographic photosensitive member using a polysilane compound, which has a low photosensitivity, but has no advantage at all when compared with conventional photosensitive members. According to the disclosure in Japanese Patent Application Laid-Open No. 3-198061, a photosensitive member having superior flexibility, film strength and adhesion can be obtained when a polysilane having a substituted or unsubstituted arylene group in its main chain is incorporated in the photosensitive layer. However, the incorporation of carbon atoms in the polysilane main chain sacrifices the high mobility inherent in polysilane.